Throttle upstream pressure estimating apparatus and cylinder charged air quantity calculating apparatus for internal combustion engine

ABSTRACT

In a non-critical pressure region where a pressure ratio [Pm/Pthrup(i−1)] of an intake air pressure Pm (throttle downstream pressure) detected by an intake air pressure sensor to a previous throttle upstream pressure Pthrup(i−1) is greater than a predetermined value B, the previous throttle upstream pressure Pthrup(i−1) is substituted for one of two terms of the throttle upstream pressures Pthrup(i) included in an intake system model so that present throttle upstream pressure Pthrup(i) is calculated. In a critical pressure region where the pressure ratio is less than or equal to the predetermined value B, a physical value f(Pm/Pthrup(i)) using a pressure ratio [Pm/Pthrup(i)] of the intake air pressure Pm to a present throttle upstream pressure Pthrup(i) as a parameter is regarded as a steady value fc so that the present throttle upstream pressure Pthrup(i) is calculated.

This application is a division of Ser. No. 12/119,781 filed May 13,2008, now U.S. Pat. No. 7,681,442, which claims priority based onJapanese Patent Application Nos. 2007-164512 filed on Jun. 22, 2007, and2007-167187 filed on Jun. 26, 2007, the entire disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a throttle upstream estimatingapparatus for an internal combustion engine which calculates an upstreamside pressure of a throttle valve by using an intake system model and toa cylinder charged air quantity calculating apparatus for the internalcombustion engine which calculates a cylinder charged air quantity.

BACKGROUND OF THE INVENTION

It is necessary to accurately perform an air-fuel ratio control (i.e., afuel injection control) in order to satisfy severe law regulationsrelating to purification of exhaust gas. In order to perform accurateair-fuel ratio control, it is necessary to accurately calculate an airquantity charged into an engine cylinder (i.e., a cylinder charged airquantity) and appropriately set a fuel injection quantity in accordancewith the cylinder charged air quantity.

In order to raise the accuracy for calculating the cylinder charged airquantity, data of the upstream side pressure of a throttle valve(hereafter referred to as “throttle upstream pressure”) is required. Inthis regard, in a naturally aspirated engine, the throttle upstreampressure is equivalent to an atmospheric pressure. However, in the caseof an engine with a supercharger, in an operation range where a chargedpressure of a supercharger is generated, the throttle upstream pressurebecomes higher than an atmospheric pressure due to the charged pressure.

Conventionally, an internal combustion engine is provided with apressure sensor to detect a throttle upstream pressure, which howeverincreases its manufacturing cost.

Among engines with superchargers, as disclosed in JP-2006-27763A andJP-2006-194107A (EP-1837512A1), a throttle upstream pressure (compressordownstream pressure) is calculated by using a compressor model(turbocharger model) in which supercharging effects by a compressor ofthe supercharger are modeled.

As disclosed in JP-2002-201998A (U.S. Pat. No. 6,497,214B2), a cylindercharged air quantity is calculated by using an equation of an intakesystem model made by modeling behaviors of an intake air during a periodwhere a change in a throttle opening degree causes a change in an actualcylinder charged air quantity. In such an internal combustion engine, inorder to reduce a CPU load for engine control by simplifying thecalculation of a throttle flow rate parameter, a map (table) of thethrottle flow rate parameter using a throttle opening degree as aparameter is stored in ROM in advance, and a throttle flow rateparameter corresponding to a present throttle opening degree is read bysearching the map.

A compressor model (turbocharger model) has many adaptation subjects.Therefore, there is required a lot of work time for the adaptation.Further, there exists great influence of manufacture dispersion of theadaptation subjects, decreasing dispersion of estimated values of thethrottle upstream pressure. Further, due to manufacture dispersion oraging of parts (throttle valve etc.) of the intake system, a throttleopening sensor, etc., there occurs a difference between a map value(adaptation value) of the throttle flow rate parameter and an actualvalue of the throttle flow rate parameter in an actual vehicle,decreasing the calculation accuracy of the cylinder charged airquantity.

SUMMARY OF THE INVENTION

The present invention is made in view of the above, and its object is toprovide a throttle upstream pressure estimating apparatus for aninternal combustion engine which is capable of securing the estimationaccuracy of the throttle upstream pressure while eliminating or reducingthe adaptation work time for a model to be used for estimating thethrottle upstream pressure. Further, another object of the presentinvention is to provide a cylinder charged air quantity calculatingapparatus for an internal combustion engine which is capable ofimproving the accuracy of a throttle flow rate parameter to be usedwhile calculating the cylinder charged air quantity by using an intakesystem model and is capable of improving the calculation accuracy of thecylinder charged air quantity while meeting the demand of reducing thecalculation load.

In order to achieve the above objects, according to the presentexemplary embodiment, there is provided intake air pressure detectingmeans which detects downstream side pressure (hereafter referred to as“intake air pressure”) Pm of a throttle valve provided in an intakepassage of an internal combustion engine and throttle upstream pressureestimating means which repeats calculating throttle upstream pressure ata predetermined time interval by using an equation of an intake systemmodel which models behaviors of an intake air during a period where achange in upstream side pressure of the throttle valve (hereafterreferred to as “throttle upstream pressure”) and a change in a throttleopening degree cause a change in the intake air pressure Pm to cause achange in an actual cylinder charged air quantity. The throttle upstreampressure estimating means substitutes a previous throttle upstreampressure Pthrup(i−1) for a part of a plurality of throttle upstreampressures included in the equation of the intake system model tocalculate a present throttle upstream pressure Pthrup(i).

According to the present exemplary embodiment, additional work time foradaptation can be eliminated or reduced by calculating a throttleupstream pressure by using the intake system model for calculating acylinder charged air quantity.

However, a plurality of terms using the throttle upstream pressure as aparameter are included in the equation of the intake system model forcalculating the cylinder charged air quantity. In particular, a functionfor calculating a physical value f(Pm/Pthrup(i)) determined based on aratio [Pm/Pthrup(i)] of the intake air pressure Pm to the presentthrottle upstream pressure Pthrup(i) is complicated. Therefore, it isdifficult to solve the equation of the intake system model for thepresent throttle upstream pressure Pthrup(i).

Therefore, according to the present exemplary embodiment, the previousthrottle upstream pressure Pthrup(i−1) is substituted for a part of aplurality of throttle upstream pressures included in the intake systemmodel and the present throttle upstream pressure Pthrup(i) iscalculated. That is, as shown in FIGS. 3 and 4, even when the downstreamside pressure of the throttle valve (hereafter referred to as “intakeair pressure”) Pm sharply changes in a step-like manner, compared withsuch a change, a change in the throttle upstream pressure is very small.Since a difference between the previous throttle upstream pressurePthrup(i−1) and the present throttle upstream pressure Pthrup(i) is verysmall, even if the previous throttle upstream pressure Pthrup(i−1) issubstituted for a part of a plurality of throttle upstream pressuresPthrup(i) included in the equation of the intake system model, the modelaccuracy can be secured. As a result, it becomes possible to accuratelycalculate the throttle upstream pressure by using the intake systemmodel for calculating the cylinder charged air quantity. Therefore,while eliminating or reducing the work time of adaptation for the modelto be used for estimating the throttle upstream pressure Pthrup(i),estimation accuracy of the throttle upstream pressure Pthrup(i) can besecured.

According to the present exemplary embodiment, in a cylinder charged airquantity calculating apparatus for an internal combustion engine whichcalculates a cylinder charged air quantity by using an equation of anintake system model including a flow rate parameter depending on athrottle opening degree (hereafter referred to as “throttle flow rateparameter”), there are provided: storage means in which a map definingthe relationship between a throttle opening degree and a throttle flowrate parameter is stored; learning means which learns, when apredetermined learning execution condition is fulfilled, a learningcorrection amount with respect to a map value based on a deviationbetween an actual value of the throttle flow rate parameter calculatedaccording to a present throttle opening degree by using the equation ofthe intake system model and the map value of the throttle flow rateparameter read from the storage means; correcting means which correctsthe map value of the throttle flow rate parameter corresponding to thepresent throttle opening degree read from the storage means during anoperating state of the internal combustion engine by using the learningcorrection amount; and cylinder charged air quantity calculating meanswhich calculates a cylinder charged air quantity by using the map valueof the throttle flow rate parameter corrected by the correcting meansduring the operating state of the internal combustion engine.

According to the present exemplary embodiment, when a predeterminedlearning execution condition is fulfilled, an actual value of thethrottle flow rate parameter (μ·A) according to the present throttleopening degree is calculated by using the equation of the intake systemmodel, a learning correction amount for a map value is learned based onthe deviation between the actual value and the map value (adaptationvalue), the map value of the throttle flow rate parameter correspondingto the present throttle opening degree is corrected by using thelearning correction amount during the operating state of the internalcombustion engine, and a cylinder charged air quantity is calculated byusing the map value after correction. With this configuration, even whenthere occurs a difference between a map value (adaptation value) of athrottle flow rate parameter and an actual value of the throttle flowrate parameter in an actual vehicle due to manufacture dispersion oraging of parts of the intake system, and the throttle opening sensor ofthe electronic throttle system, the map value of the throttle flow rateparameter can properly be corrected by using the learning correctionamount based on the deviation between the actual value and the mapvalue. As a result, it becomes possible to improve the accuracy of thethrottle flow rate parameter by simple processing, to improve thecalculation accuracy of the cylinder charged air quantity while meetingthe demand of reducing the calculation load, and to reduce dispersion indrivability of vehicles and dispersion in emission.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description made withreference to the accompanying drawing, in which like parts aredesignated by like reference numbers and in which:

FIG. 1 is a schematic diagram showing an overall arrangement of anengine control system in accordance with one embodiment of the presentinvention;

FIG. 2A shows a map of a physical value f(Pm/Pthrup(i)) determined basedon a ratio [Pm/Pthrup(i)] of an intake air pressure Pm to a throttleupstream pressure Pthrup(i); and FIG. 2B shows an inverse transform mapf{f(Pm/Pthrup(i))} of the physical value f(Pm/Pthrup(i));

FIG. 3 is a time chart showing behaviors of an intake air pressure Pm(throttle downstream pressure) and a throttle upstream pressure during atransient state in a full-load region;

FIG. 4 is a time chart showing behaviors of an intake air pressure Pm(throttle downstream pressure) and a throttle upstream pressure during atransient state in a partial-load region;

FIG. 5 is a flowchart showing a throttle upstream pressure estimatingmain routine;

FIG. 6 is a flowchart showing a throttle upstream pressure estimatingroutine in a critical pressure region;

FIG. 7 is a flowchart showing a throttle upstream pressure estimatingroutine in a non-critical pressure region;

FIG. 8 is a flowchart showing a throttled air quantity calculatingroutine on the basis of the intake air pressure;

FIG. 9 is a flowchart showing a volumetric efficiency η calculatingroutine;

FIG. 10 is a flowchart showing an f(Pm/Pthrup(i−1)) calculating routinein a critical pressure region;

FIG. 11 is a flowchart showing a throttle flow rate parameter μ·Acalculating routine;

FIG. 12 is a diagram for explaining the relation between an intake airquantity and a throttle upstream pressure;

FIG. 13 is a flowchart showing a throttle flow rate parameter learningcorrection amount learning routine;

FIG. 14 is a diagram for explaining classification of the learningregion according to a throttle opening degree; and

FIG. 15 is a time chart showing a difference between an estimated valueof the throttle upstream pressure Pthrup estimated by using an intakesystem model and an actual value (simulation value) and learningcorrection effects.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a preferred embodiment in which the present invention is applied toan internal combustion engine having a supercharger will be described.

First, with reference to FIG. 1, a schematic configuration of an overallarrangement of an engine control system will be described. An aircleaner 13 is provided at an upstream end of an intake pipe 12 (intakepassage) of the engine 11, which is an internal combustion engine. Anairflow meter 14, provided on a downstream side of the air cleaner 13,measures an intake air quantity. The airflow meter 14 is provided withan intake air temperature sensor (not shown) which detects an intake airtemperature T.

There are provided, on a downstream side of the airflow meter 14, acompressor 27 of a supercharger 25 of an exhaust turbine type (to bedescribed later) and an intercooler 31 which cools an intake airpressurized by the compressor 27. Provided on the downstream side of theintercooler 31 are a throttle valve 15 of which opening degree iscontrolled by a motor etc. and a throttle opening sensor 16 whichdetects a throttle opening degree.

A surge tank 17 is disposed on the downstream side of the throttle valve15. An intake air pressure sensor 18 for detecting a downstream sidepressure (hereafter referred to as “intake air pressure”) Pm of thethrottle valve 15 is provided in the surge tank 17. To the surge tank17, an intake manifold 19 for introducing air into the cylinders of theengine 11 is connected. In the intake manifold 19, a fuel injectionvalve 20 for injecting fuel is attached near an intake port of eachcylinder.

Spark plugs 21 are attached to respective cylinder heads of the engine11, and the mixture in each cylinder is ignited by spark dischargeoccurring at each of the spark plugs 21. Further, the engine 11 isprovided with variable valve timing units 43 and 44 for varying theopening and closing timing (valve timing) VVT of the intake valve 41 andexhaust valve 42 according to an engine operating condition. Also, theconstruction may be such that the variable valve timing unit 43 on theintake side alone is provided and the variable timing unit 44 on theexhaust side may be omitted. The variable valve timing units 43 and 44on both the intake and exhaust sides may be omitted.

On the other hand, the exhaust pipe 22 (exhaust passage) of the engine11 is provided with an air-fuel ratio sensor 24 for detecting an airfuel ratio of the exhaust gas. On the downstream side of the air-fuelratio sensor 24, there is provided a catalyst 23, such as a three-waycatalyst, for purifying the exhaust gas.

The engine 11 is provided with a supercharger 25 of an exhaust turbinetype. An exhaust turbine 26 is provided in the exhaust pipe 22 betweenthe air-fuel ratio sensor 24 and the catalyst 23. A compressor 27 isprovided in the intake pipe 12 between the airflow meter 14 and thethrottle valve 15. The exhaust turbine 26 and the compressor 27 areconnected with each other. The compressor 27 is rotated by rotating theexhaust turbine 26 by kinetic energy of the exhaust gas to superchargethe intake air.

Further, the intake pipe 12 is provided with, on the upstream side ofthe throttle valve 15, an intake bypass passage 28 for bypassing theupstream side and the downstream side of the compressor 27. There isprovided, midway along the intake bypass passage 28, an air bypass valve(hereafter referred to as “ABV”) 29 for opening and closing the intakebypass passage 28. By controlling a vacuum switching valve 30 for ABV,the opening and closing operation of ABV 29 is controlled.

The exhaust pipe 22 is provided with an exhaust bypass passage 32 forbypassing the upstream side and the downstream side of the exhaustturbine 26. A waste gate valve (hereafter referred to as “WGV”) foropening and closing the exhaust bypass passage 32 is provided midwayalong the exhaust bypass passage 32. WGV 33 is constructed such that itsopening degree is controlled when an actuator 35 of a diaphragm type iscontrolled by controlling a vacuum switching valve 34 for WGV.

Further, there are mounted on a cylinder block of the engine 11, acooling temperature sensor 36 for detecting a cooling temperature Thwand a crank angle sensor 37 for outputting a pulse signal everypredetermined crank angle with rotation of a crank shaft of the engine11. According to the signal outputted from the crank angle sensor 37, acrank angle and an engine rotational speed Ne are detected. Anatmospheric pressure sensor 39 for detecting an atmospheric pressure isalso provided.

Various detection signals of the sensors are inputted to an enginecontrol circuit (hereafter referred to as ECU) 38. ECU 38 is constructedby using a microcomputer as a main body. By executing various enginecontrol routines stored in its ROM (storage medium), ECU 38 controls afuel injection quantity, ignition timing, and the like. At the sametime, ECU 38 controls the rotation of the exhaust turbine 26 and thecompressor 27 to control a charged pressure by controlling an openingdegree of WGV 33 to control an exhaust gas amount supplied to theexhaust gas turbine 26.

Further, by using an equation of the intake system model made bymodeling behaviors of the intake air during a period where a change inan upstream side pressure of a throttle valve 15 (hereafter referred toas “throttle upstream pressure”) and a change in a throttle openingdegree cause a change in an intake air pressure Pm to cause a change inan actual cylinder charged air quantity, ECU 38 calculates the throttleupstream pressure at a predetermined cycle.

In intake system models for calculating the cylinder charged airquantity, an equation for calculating a throttled air quantity isexpressed by Equation (1) below.

$\begin{matrix}{{Gin} = {\mu \cdot A \cdot \frac{{Pthrup}(i)}{\sqrt{R \cdot T}} \cdot {f\left( {{Pm}/{{Pthrup}(i)}} \right)}}} & (1)\end{matrix}$

Gin: throttled air quantity [kg/sec]

μ: flow coefficient

A: effective cross-section area of throttle opening [m²]

Pthrup(i): throttle upstream pressure [Pa]

Pm: intake air pressure [Pa]

R: gas constant

T: intake air temperature [K]

F(Pm/Pthrup(i)): Physical value determined based on Pm/Pthrup(i)A=πr ²(1−cos² θ)  (2)

r: radius of throttle valve [m]

θ: throttle opening degree

For finding a physical value f(Pm/Pthrup(i)) determined based on a ratio[Pm/Pthrup(i)] of the intake air pressure Pm to the throttle upstreampressure Pthrup(i), either Equation (3) or Equation (4) below isselected in accordance with the pressure ratio [Pm/Pthrup(i)].

$\begin{matrix}{{{{In}\mspace{14mu}{case}\mspace{14mu}{of}\mspace{14mu}{{Pm}/{{Pthrup}(i)}}} \leq \left( \frac{2}{\kappa + 1} \right)^{\frac{\kappa}{\kappa - 1}}}{{f\left( {{Pm}/{{Pthrup}(i)}} \right)} = {\sqrt{\kappa \cdot \left( \frac{2}{\kappa + 1} \right)^{\frac{\kappa + 1}{\kappa - 1}}} = {{steady}\mspace{14mu}{value}\mspace{14mu}{fc}}}}} & (3) \\{{{{In}\mspace{14mu}{case}\mspace{14mu}{of}\mspace{14mu}{{Pm}/{{Pthrup}(i)}}} > \left( \frac{2}{\kappa + 1} \right)^{\frac{\kappa}{\kappa - 1}}}{{f\left( {{Pm}/{{Pthrup}(i)}} \right)} = \sqrt{\frac{2\kappa}{\kappa - 1}\begin{Bmatrix}{\left( \frac{Pm}{{Pthrup}(i)} \right)^{\frac{2}{\kappa}} -} \\\left( \frac{Pm}{{Pthrup}(i)} \right)^{\frac{\kappa + 1}{\kappa}}\end{Bmatrix}}}\left( {\kappa\text{:}\mspace{14mu}{ratio}\mspace{14mu}{of}\mspace{14mu}{specific}\mspace{14mu}{heat}} \right)} & (4)\end{matrix}$

In the equation of the intake system model represented by Equation (1),there are included two terms using the throttle upstream pressurePthrup(i) as a parameter. In particular, the functional equations (3)and (4) for calculating the physical value f(Pm/Pthrup(i)) determinedbased on the pressure ratio [Pm/Pthrup(i)] are complicated. Therefore,it is difficult to solve the equation of the intake system model for thethrottle upstream pressure Pthrup(i).

Therefore, in the present embodiment, the previous throttle upstreampressure Pthrup(i) is substituted for one of the throttle upstreampressures Pthrup(i) of two terms included in the intake system model tocalculate the present throttle upstream pressure Pthrup(i). That is, asshown in FIGS. 3 and 4, during a transient state, even when the intakeair pressure Pm (a throttle downstream pressure) sharply changes in astep-like manner, compared with such a change, a change in the throttleupstream pressure is very small. Since a difference between the previousthrottle upstream pressure (i−1) and the present throttle upstreampressure Pthrup(i) is very small, even if the previous throttle upstreampressure Pthrup(i−1) is substituted for one of the throttle upstreampressures Pthrup(i) of the two terms included in the intake systemmodel, accuracy of the model can be secured.

In this case, as an equation of the intake system model for calculatingthe throttle upstream pressure Pthrup(i), Equation (5) below is used.

$\begin{matrix}{{Gin} = {\mu \cdot A \cdot \frac{{Pthrup}\left( {i - 1} \right)}{\sqrt{R \cdot T}} \cdot {f\left( {{Pm}/{{Pthrup}(i)}} \right)}}} & (5)\end{matrix}$

Gin: throttled air quantity [kg/sec]

μ: flow coefficient

A: effective cross-section area of throttle opening [m²]

Pthrup(i−1): previous throttle upstream pressure [Pa]

Pthrup(i): present throttle upstream pressure [Pa]

Pm: intake air pressure [Pa]

R: gas constant

T: intake temperature [K]

f(Pm/Pthrup(i)): physical value determined based on Pm/Pthrup(i)

In Equation (5), a function for calculating the physical valuef(Pm/Pthrup(i)) determined based on the ratio [pm/Pthrup(i)] of theintake air pressure Pm to the present throttle upstream pressurePthrup(i) is complicated. Therefore, first, by using Equation (6)obtained by transforming Equation (5), the physical valuef(Pm/Pthrup(i)) is calculated.

$\begin{matrix}{{f\left( {{Pm}/{{Pthrup}(i)}} \right)} = \frac{Gin}{\left( {\mu \cdot {A/\sqrt{R \cdot T}}} \right) \cdot {{Pthrup}\left( {i - 1} \right)}}} & (6)\end{matrix}$

Gin: throttled air quantity [kg/sec]

μ: flow coefficient

A: effective cross-section area of throttle opening [m²]

R: gas constant

T: intake temperature [K]

Pthrup(i−1): previous throttle upstream pressure [Pa]

After calculating the physical value f(Pm/Pthrup(i)), by using aninverse transform map f{f(Pm/Pthrup(i))} shown in FIG. 2B, a pressureratio [Pm/Pthrup(i)] corresponding to a calculation value of thephysical value f(Pm/Pthrup(i)) is calculated, and the present throttleupstream pressure Pthrup(i) is calculated by the following equation.Pthrup(i)=Pm/f(f(Pm/Pthrup(i)))  (7)

As shown in FIG. 2A, in a region where a pressure ratio [Pm/Pthrup(i)]is equal to or smaller than a predetermined value B, the physical valuef(Pm/Pthrup(i)) determined based on the pressure ratio [Pm/Pthrup(i)]becomes a steady value fc.

A region where the pressure ratio [Pm/Pthrup(i)] at which the physicalvalue f(Pm/Pthrup(i)) becomes the steady value fc is equal to or smallerthan the predetermined value B is called a “critical pressure region”and a region where the pressure ratio is greater than the predeterminedvalue B is called a “non-critical pressure region.” The predeterminedvalue B is defined by the following Equation (8).

$\begin{matrix}{{B = \left( \frac{2}{\kappa + 1} \right)^{\frac{\kappa}{\kappa - 1}}}\left( {\kappa\text{:}\mspace{14mu}{ratio}\mspace{14mu}{of}\mspace{14mu}{specific}\mspace{14mu}{heat}} \right)} & (8)\end{matrix}$

In consideration of the property of the physical value f(Pm/Pthrup(i)),in the non-critical region where a ratio [Pm/Pthrup(i−1)] of the intakeair pressure Pm detected by the intake air pressure sensor 18 to theprevious throttle upstream pressure Pthrup(i−1) is greater than thepredetermined value B, by using Equations (5) and (6) including theprevious throttle upstream Pthrup(i−1), the present throttle upstreampressure Pthrup(i) is calculated.

In the critical pressure region where the previous pressure ratio[Pm/Pthrup (i−1)] is equal to or smaller than the predetermined value B,it is regarded that the physical value f(Pm/Pthrup(i)) determined basedon the ratio [Pm/Pthrup(i)] of the intake air pressure Pm to the presentthrottle upstream pressure Pthrup(i) is the steady value fc, and thepresent throttle upstream pressure Pthrup(i) is calculated by Equation(9) below.

$\begin{matrix}{{{Pthrup}(i)} = \frac{Gin}{\left( {\mu \cdot {A/\sqrt{R \cdot T}}} \right) \cdot {fc}}} & (9)\end{matrix}$

Gin: throttled air quantity [kg/sec]

μ: flow coefficient

A: effective cross-sectional area of throttle opening [m²]

R: gas constant

T: intake air temperature [K]

fc: steady value

With the above arrangement, in accordance with the pressure ratio[Pm/Pthrup(i)], two equations for calculating the present throttleupstream pressure Pthrup(i) can be switched appropriately, and thepresent throttle upstream pressure Pthrup(i) can be calculated with highaccuracy.

As an initial value of the previous throttle upstream pressurePthrup(i−1), an intake air pressure Pm detected by the intake airpressure sensor 18 immediately before the startup of the engine is used.That is, when the engine is stopped, the intake passage on both theupstream and downstream sides of the throttle valve 15 is filled withair of atmospheric pressure. Therefore, a value equivalent to theatmospheric pressure may be used as the initial value of the previousthrottle upstream pressure Pthrup(i−1). Also, the intake air pressure Pmdetected by the intake air pressure sensor 18 immediately before thestartup of the engine is a value equivalent to the atmospheric pressure.Therefore, as the initial value of the previous throttle upstreampressure Pthrup(i−1), the intake air pressure Pm immediately before thestartup of the engine can be used.

The calculation of the above-described throttle upstream pressurePthrup(i) is executed by ECU 38 according to routines of FIGS. 5 to 11.Now, processing in each routine will be described.

[Throttle Upstream Pressure Estimating Main Routine]

The throttle upstream pressure estimating main routine of FIG. 5 isexecuted at a predetermined cycle while ECU 38 is turned on. In Step101, the intake air pressure Pm detected by the intake air pressuresensor 18, intake temperature T, engine rotational speed Ne, valvetiming VVT, cooling temperature Thw, etc. are read.

After that, the process advances to Step 102 in which it is determinedwhether it is a critical pressure region where the ratio [Pm/Pthrup(i−1)] of the intake air pressure Pm to the previous throttle upstreampressure Pthrup (i−1) is less than or equal to the predetermined value B(see FIG. 2A). The intake air pressure Pm detected by the intake airpressure sensor 18 immediately before the startup of the engine is usedas an initial value of the previous throttle upstream pressurePthrup(i−1)

In Step 102, if it is determined that it is in the critical pressureregion (Pm/Pthrup (i−1)≦B), the process advances to Step 103 in which athrottle upstream pressure estimating routine in the critical pressureregion is executed. FIG. 6 shows the throttle upstream pressureestimating routine in the critical pressure region. When it isdetermined that it is in a non-critical pressure region(Pm/Pthrup(i−1)>B), the process advances to Step 104 in which a throttleupstream pressure estimating routine in the non-critical pressure regionis executed. FIG. 7 shows the throttle upstream pressure estimatingroutine in the non-critical pressure region.

[Throttle Upstream Pressure Estimating Routine in Critical PressureRegion]

The throttle upstream pressure estimating routine in the criticalpressure region of FIG. 6 is a subroutine, executed in Step 103, of thethrottle upstream pressure estimating main routine of FIG. 5. In Step201, a throttled air quantity calculating routine shown in FIG. 8 isexecuted. Based on the intake air pressure Pm detected by the intake airpressure sensor 18, a throttled air quantity Gin is calculated.

After that, the process advances to Step 202, and an f(Pm/Pthrup(i−1))calculating routine shown in FIG. 10 is executed to calculate a physicalvalue f(Pm/Pthrup(i−1)) in the critical pressure region. The physicalvalue f(Pm/Pthrup (i−1)) in the critical pressure region is a steadyvalue fc. Then, the process advances to Step 203 in which the throttleflow rate parameter μ·A is calculated by executing a throttle flow rateparameter μ·A calculating routine shown in FIG. 11.

After that, the process advances to Step 204 in which by using thephysical value f(Pm/Pthrup(i−1)) in the critical pressure region, thepresent throttle upstream pressure Pthrup(i) is calculated by followingEquation (10).

$\begin{matrix}{{{{Pthrup}(i)} = \frac{Gin}{\left( {\mu \cdot {A/\sqrt{R \cdot T}}} \right) \cdot {f\left( {{Pm}/{{Pthrup}\left( {i - 1} \right)}} \right)}}}{{f\left( {{Pm}/{{Pthrup}\left( {i - 1} \right)}} \right)} = {{steady}\mspace{14mu}{value}\mspace{14mu}{fc}}}} & (10)\end{matrix}$[Throttle Upstream Pressure Estimating Routine in Non-Critical PressureRegion]

The throttle upstream pressure estimating routine in the non-criticalpressure region of FIG. 7 is a subroutine, executed in Step 104, of thethrottle upstream pressure estimating main routine of FIG. 5. In Step301, the throttled air quantity calculating routine shown in FIG. 8 isexecuted to calculate the throttled air quantity Gin based on the intakeair pressure Pm detected by the intake air pressure sensor 18.

Subsequently, the process advances to Step 302. By using the previousthrottle upstream pressure Pthrup(i−1), the physical valuef(Pm/Pthrup(i)) determined based on a pressure ratio [Pm/Pthrup(i)] iscalculated by the following Equation (11).

$\begin{matrix}{{f\left( {{Pm}/{{Pthrup}(i)}} \right)} = \frac{Gin}{\left( {\mu \cdot {A/\sqrt{R \cdot T}}} \right) \cdot {{Pthrup}\left( {i - 1} \right)}}} & (11)\end{matrix}$

After that, the process advances to Step 303, and by using the inversetransform map f{f(Pm/Pthrup(i))} of the physical value f(Pm/Pthrup(i))shown in FIG. 2B, a pressure ratio [Pm/Pthrup(i)] corresponding to acalculated value of the physical value f(Pm/Pthrup(i)) is calculated,and the present throttle upstream pressure Pthrup(i) is calculated bythe following Equation.Pthrup(i)=Pm/f{f(Pm/Pthrup(i))}[Throttled Air Quantity Calculating Routine Based on Intake AirPressure]

The throttled air quantity calculating routine based on the intake airpressure of FIG. 8 is a subroutines executed in Step 201 of FIG. 6 andStep 301 of FIG. 7. In Step 401, based on the intake air pressure Pm, anair quantity Qm downstream of the throttle valve in the intake passageis calculated by the following Equation (12).Qm=Pm·Vim/(R·T)  (12)

where Vim represents a volume of the intake passage downstream of thethrottle valve 15, R represents the gas constant, and T represents theintake air temperature.

Subsequently, the process advances to Step 402. By executing avolumetric efficiency η calculating routine shown in FIG. 9, volumetricefficiency η is calculated. In Step 403, by using the volumetricefficiency η, a model time constant τIM is calculated by the followingEquation (13).τIM=2·Vim/(Vc·η·Ne/60)  (13)

where Vim represents a volume of intake passage downstream of thethrottle valve 15, Vc represents a volume of the cylinder, and Nerepresents an engine speed (rpm).

After that, the process advances to Step 404. By using the model timeconstant τIM, a throttled air quantity Gin based on the intake airpressure Pm is calculated by the following equation.Gin={Qm(i)−Qm(i−1)}/Ts+Qm(i−1)/τIM  (14)

where Qm(i) represents a present air quantity in the intake passagedownstream of the throttle valve 15, Qm(i−1) represents a previous airquantity in the intake passage downstream of the throttle valve 15, andTs represents a sampling time.

[Volumetric Efficiency η Calculating Routine]

The volumetric efficiency η calculating routine shown in FIG. 9 is asubroutine, which is executed in Step 402 of the throttled air quantitycalculating routine. In Step 501, according to a volumetric efficiencymap using the pressure ratio [Pm/Pthrup(i−1)], engine rotational speedNe, and valve timing VVT as parameters, the base volumetric efficiencyηr according to the present engine operating condition is calculated.Then, the base volumetric efficiency ηr is corrected by using acorrection value corresponding to the coolant temperature Thw to obtainthe volumetric efficiency η.

[f(Pm/Pthrup(i−1)) Calculating Routine in Critical Pressure Region]

The f(Pm/Pthrup(i−1)) calculating routine in the critical pressureregion shown in FIG. 10 is a subroutine, executed in Step 202 of thethrottle upstream pressure estimating routine. In Step 601, the physicalvalue f(Pm/Pthrup(i−1)) in the critical pressure region is calculated bythe following Equation (15).

$\begin{matrix}{{f\left( {{Pm}/{{Pthrup}\left( {i - 1} \right)}} \right)} = {\sqrt{{\kappa\left( \frac{2}{\kappa + 1} \right)}^{\frac{\kappa + 1}{\kappa - 1}}} = {{steady}\mspace{14mu}{value}\mspace{14mu}{{fc}\left( {\kappa\text{:}\mspace{14mu}{ratio}\mspace{14mu}{of}\mspace{14mu}{specific}\mspace{14mu}{heat}} \right)}}}} & (15)\end{matrix}$

Since the physical value f(Pm/Pthrup(i−1)) in the critical pressureregion is a steady value fc, the steady value fc calculated by the aboveequation in advance may be stored in ROM of ECU 38.

[Throttle Flow Rate Parameter η·A Calculating Routine]

The throttle flow rate parameter μ·A calculating routine shown in FIG.11 is a subroutine, executed in Step 203 of the throttle upstreampressure estimating routine. In Step 701, a present throttle openingdegree θ is read. Then, in subsequent Step 702, a map of the throttleflow rate parameter μ·A using the throttle opening degree as a parameteris searched, and a throttle flow rate parameter μ·A corresponding to thepresent throttle opening degree θ is calculated.

Also, an effective cross-sectional area A of the throttle opening may becalculated from the present throttle opening degree θ by Equation (2),and the throttle flow rate parameter μ·A may be found by multiplying theeffective cross-sectional area A of the throttle opening with a flowcoefficient μ.

The present throttle upstream pressure Pthrup(i) estimated by theroutines in FIGS. 5 to 11 described above is used when estimating acylinder charged air quantity by using the intake system model.

In the present embodiment described above, as shown in FIGS. 3 and 4, inconsideration of the fact that, during a transient state, even when theintake air pressure Pm changes sharply in a step-like manner, a changein the throttle upstream pressure is small in comparison with the changein the intake air pressure Pm and a difference between the previousthrottle upstream pressure Pthrup(i−1) and the present throttle upstreampressure Pthrup(i) is very small, by substituting the previous throttleupstream pressure Pthrup(i−1) for one of the throttle upstream pressuresPthrup(i) of two terms included in the equation of the intake systemmodel, it becomes possible to solve the equation of the intake systemmodel for the present throttle upstream pressure Pthrup(i) whilesecuring accuracy of the model. Accordingly, it becomes possible tocalculate the throttle upstream pressure Pthrup(i) with high accuracy byusing the intake system model that calculates a cylinder charged airquantity. Therefore, it is possible to secure the estimation accuracy ofthe throttle upstream pressure Pthrup(i) while eliminating or reducingthe adaptation work time for the model to be used for estimating thethrottle upstream pressure Pthrup(i).

Next, the charged air quantity Gcf is calculated by using the intakesystem model in the following manner.

The following relationship is derived when the law of mass conservationis applied to the flow of intake air flowing in an intake passageconnecting from the throttle valve 15 to an intake port of the engine 11(hereafter referred to as “throttle downstream intake passage”).d/dt·Qm=Gin−Gcf  (16)

where Qm represents an air quantity in the throttle downstream intakepassage, d/dt·Qm represents a change of the air quantity in the throttledownstream intake passage, Gin represents the throttled air quantity,and Gcf represents the cylinder charged air quantity.

Furthermore, the following relationship is derived when the equation ofgas state is applied to the throttle downstream passage.Gcf=η·(Ne/2)·Vc·(Qm/VIM)  (17)

η: volumetric efficiency

Ne: engine speed [rps]

Vc: cylinder volume [m³]

VIM: volume of throttle downstream intake passage [m³]

The volumetric efficiency η is variable depending on an intake air flowrate. Therefore, the volumetric efficiency η is obtained from a map etc.defined by engine speed Ne and intake air pressure Pm which are theparameters correlating with the intake air flow rate.η=f(Ne,Pm)  (18)

Furthermore, the time constant τIM of the intake system model is definedby the following Equation.τIM=2·VIM/(Vc·η·Ne)  (19)

The following Equation is derived from the above Equations (16) to (19).d/dt·Qm=Gin−Qm/τIM  (20)

As the above Equation (20) is an equation of continuity, in order toenable ECU 38 to calculate it, it can be converted into the followingdiscreet Equation (21).{Qm(i)−Qm(i−1)}/Ts=Gin(i)−Qm(i−1)/τIM  (21)

where Ts is a sampling time.

The Equation (21) can be modified in the following manner to derive theair quantity Qm in the throttle downstream intake passage.Qm(i)={Gin(i)−Qm(i−1)/τIM}·Ts+Qm(i−1) [kg]  (22)

Moreover, the following Equation for calculating the intake air pressurePm based on the air quantity Qm in the throttle downstream intakepassage is derived when the Equation of gas state is applied to thethrottle downstream intake passage.Pm=Qm·R·T/VIM [Pa]  (23)

R: gas constant

T: intake temperature

The following relationship is derived from the above Equations (23) and(17) to obtain the cylinder charged air quantity Gcf.Gcf=η·Vc·Pm/(2·R·T) [kg/rev]  (24)

ECU 38 calculates the cylinder charged air quantity Gcf by usingEquation (24) derived from each equation of the above-described intakesystem model.

It becomes possible by using Equation (2) that an effectivecross-section area A of the throttle opening is calculated from athrottle opening degree θ, and the throttle opening effectivecross-section area A is multiplied with a flow coefficient μ to find aflow rate parameter (hereafter referred to as “throttle flow rateparameter”) μ·A depending on the throttle opening degree θ. In thepresent embodiment, however, in order to simplify calculation of thethrottle flow rate parameter μ·A to reduce the CPU load of ECU 38, a map(table) of adaptation values of the throttle flow rate parameter μ·Ausing the throttle opening degree θ as a parameter is stored in ROM(storage means) of ECU 38 in advance and, by searching the map, athrottle flow rate parameter μ·A corresponding to the present throttleopening degree θ is read.

However, when a cylinder charged air quantity Gcf is calculated by usinga map value (adaptation value) of the throttle flow rate parameter μ·Aas it is, due to manufacture dispersion or aging of parts (throttlevalve 15 etc.) of the intake system, the throttle opening sensor 16,etc., a difference is caused between the map value (adaptation value) ofthe throttle flow rate parameter μ·A and an actual value of the throttleflow rate parameter μ·A in an actual vehicle, degrading the calculationaccuracy of the cylinder charged air quantity Gcf.

In the present invention, therefore, during an engine operating state,the map value of the throttle flow rate parameter μ·A is learned andcorrected as follows.

First, when a predetermined learning execution condition is satisfiedduring the engine operating state, by using Equation (25) below derivedfrom the equation for calculating the throttled air quantity of theintake system model, an actual value of the throttle flow rate parameterμ·A according to the present throttle opening degree θ is calculated.

$\begin{matrix}{{\mu \cdot A} = \frac{{Gin} \cdot \sqrt{R \cdot T}}{{Pthrup} \cdot {f\left( {{Pm}/{Pthrup}} \right)}}} & (25)\end{matrix}$

Then, based on a deviation between the actual value of the throttle flowrate parameter μ·A calculated by the above Equation and the map value, alearning correction amount corresponding to the map value is learned.Further, during the engine operating state, the map value of thethrottle flow rate parameter μ·A according to the present throttleopening degree θ is corrected by using the above learning correctionamount and, by using the corrected map value, a throttled air quantityGin is calculated to calculate the cylinder charged air quantity Gcf.

In the present embodiment, considering that the engine 11 is equippedwith the supercharger 25, as a learning execution condition of thelearning correction amount of the throttle flow rate parameter μ·A, thefollowing three conditions (1) to (3) are set. When these threeconditions (1) to (3) are all satisfied, the learning executioncondition is fulfilled.

(1) The engine operating condition is a steady operation in which achange in the intake air flow rate is small.

(2) Being in a low air quantity region where an intake air flow rate isequal to or smaller than a predetermined value C.

(3) The ratio Pm/Pthrup of the throttle downstream pressure Pm to thethrottle upstream pressure Pthrup is less than or equal to apredetermined value B.

With respect to Condition (1), during a steady operation state where achange in the intake air flow rate is small, a state where therelationship between the throttle opening degree θ and the throttle flowrate parameter μ·A is regarded to be substantially constant continues.Thus, being a steady operation state is defined as one of the conditionsnecessary for calculating, by using Equation (25) derived from theequation for calculating the throttled air quantity of the intake systemmodel, the actual value of the throttle flow rate parameter μ·A withhigh accuracy.

Further, with respect to Condition (2), in an operation range where acharged pressure by the supercharger 25 occurs, due to the chargedpressure, the throttle upstream pressure Pthrup becomes higher than anatmospheric pressure. Therefore, a throttle upstream pressure sensor fordetecting the throttle upstream pressure Pthrup is required, or it isnecessary to estimate the throttle upstream pressure Pthrup. However, asshown in FIG. 12, in a low air quantity region where the intake air flowrate is equal to or smaller than a predetermined value C, the chargedpressure by the supercharger 25 hardly occurs, and the throttle upstreampressure Pthrup becomes substantially equivalent to an atmosphericpressure. Therefore, it becomes possible to use a detection value of theatmospheric pressure sensor 39 as a throttle upstream pressure Pthrup.From this viewpoint, in the engine 11 equipped with the supercharger 25,as a learning execution condition, being in a low air quantity regionwhere the intake air quantity is equal to or smaller than thepredetermined value C is defined as Condition (2).

Further, in Equation (25) for calculating the throttle flow rateparameter μ·A, the physical value f(Pm/Pthrup) determined based on aratio Pm/Pthrup of the throttle downstream pressure Pm to the throttleupstream pressure Pthrup becomes a steady value fc in a criticalpressure region where the pressure ratio Pm/Pthrup is less than or equalto a predetermined value B (see FIG. 2A). In the critical pressureregion, when approximating the throttle upstream pressure Pthrup by thedetection value of the atmospheric pressure sensor 39, an approximationerror can be eliminated to some extent. From this viewpoint, in theengine 11 equipped with the supercharger 25, as a learning executioncondition, the pressure ratio Pm/Pthrup being less than or equal to thepredetermined value B is defined as Condition (3).

When a throttle opening degree θ changes, the throttle flow rateparameter μ·A also changes. As a result, the deviation between the mapvalue of the throttle flow rate parameter μ·A and the actual value alsochanges according to a change in the throttle opening degree θ.

In view of the above, in the present embodiment, as shown in FIG. 14,the region of the throttle opening degree θ from the fully closed tofully opened state is divided into a plurality of learning regions Ti(i=1 to 4), and for each learning region Ti, based on the deviationbetween the map value of the throttle flow rate parameter μ·A and theactual value, a learning correction amount is learned. With thisarrangement, it is possible to learn a learning correction amount bydividing the region of the throttle opening degree θ from the fullyclosed to fully opened state into regions Ti where the deviation betweenthe map value of the throttle flow rate parameter μ·A and the actualvalue is substantially the same, improving the learning accuracy of thelearning correction amount.

The processing for learning the learning correction amount of thethrottle flow rate parameter μ·A described above is executed by ECU 38as follows according to the throttle flow rate parameter learningcorrection amount learning routine shown in FIG. 13. The routine isexecuted during the engine operating condition at a predetermined cycle.

In Step 1101, it is determined whether the learning execution conditionis fulfilled based on whether the following three conditions are allsatisfied.

(1) Being in a steady operation state where a change in the intake airflow rate is small.

(2) Being in a low air quantity region where the intake air flow rate isless than or equal to the predetermined value C.

(3) The ratio Pm/Pthrup of the throttle downstream pressure Pm to thethrottle upstream pressure Pthrup is less than or equal to thepredetermined value B.

Of the three conditions (1) to (3), if there is at least one conditionwhich is not satisfied, the learning execution conditions is notestablished, and the routine is ended without the rest of the processingbeing executed.

In contract, when the three conditions (1) to (3) are all satisfied, thelearning execution condition is fulfilled. Therefore, the processadvances to Step 1102, and it is determined which learning region Ti(i=1 to 4) of FIG. 14 the present throttle opening degree θ detected bythe throttle opening sensor 16 corresponds to.

In the present embodiment, considering that the smaller the throttleopening degree θ is, the relatively greater the influence of thedeviation between the map value of the throttle flow rate parameter μ·Aand the actual value becomes, it is set such that the smaller thethrottle opening degree θ is, the narrower the learning region Tibecomes. As a result, it is set such that the smaller the throttleopening degree θ is, the higher the accuracy of the learning correctionamount becomes.

In Step 1103, by using Equation (26) below, an actual value of thethrottle flow rate parameter μ·A corresponding to the present throttleopening degree θ is calculated.

$\begin{matrix}{{\mu \cdot A} = \frac{{Gin} \cdot \sqrt{R \cdot T}}{{Pthrup} \cdot {f\left( {{Pm}/{Pthrup}} \right)}}} & (26)\end{matrix}$

In this case, the operation region where the learning executioncondition is fulfilled is a critical pressure region where a ratioPm/Pthrup of the throttle downstream pressure Pm to the throttleupstream pressure Pthrup is less than or equal to the predeterminedvalue B. Therefore, the physical value f(Pm/Pthrup) determined based onthe pressure ratio Pm/Pthrup is a steady value fc. Also, the operationregion where the learning execution condition is fulfilled is a low airquantity region where the intake air flow rate is less than or equal tothe predetermined value C. Therefore, there occurs little chargedpressure of the supercharger 25, and the throttle upstream pressurePthrup is substantially equal to an atmospheric pressure. Therefore, itbecomes possible to use the detection value of the atmospheric pressuresensor 39 as a throttle upstream pressure Pthrup. As a result, even ifthe throttle upstream pressure sensor is not provided, by using Equation(26), an actual value of the throttle flow rate parameter μ·Acorresponding to the present throttle opening degree θ can easily andaccurately be calculated.

After that, the process advances to Step 1104 and the map of thethrottle flow rate parameter μ·A stored in ROM (storage means) of ECU 38is searched. Then, a map value of the throttle flow rate parameter μ·Acorresponding to the present throttle opening degree θ is read, and thedeviation D between the map value and the actual value of the throttleflow rate parameter μ·A is calculated.Deviation D=Map value−Actual value

After that, the process advances to Step 1105, and it is determinedwhether the deviation D is greater than or equal to a predeterminedvalue K1 (whether or not the map value is greater than the actual valueby the predetermined value K1 or greater). When the deviation D isgreater than or equal to the predetermined value K1, the processadvances to Step 1106, and the value obtained by subtracting apredetermined value K2 from the previous learning correction amount(n−1) is updated and stored in a rewritable nonvolatile memory such asbackup RAM of ECU 38 as a present learning correction amount (n). Thus,the learning correction amount (n) of the learning region Ticorresponding to the present throttle opening degree θ is updated. Inthis regard, the relationship between the predetermined values K1 and K2used in Steps 1105 and 1106 are set as: K1>K2>0.

When a state where the deviation D is greater than or equal to thepredetermined value K1 (state where the map value is greater than theactual value by the predetermined value K1 or greater) continues, thelearning processing in Step 1106 is repeated, and the learningcorrection amount (n) gradually increases in the negative direction.

In Step 1105, when it is determined that the deviation D is smaller thanthe predetermined value K1, the process advances to Step 1107 and it isdetermined whether the deviation D is less than or equal to apredetermined value “−K3” (whether the map value is smaller than theactual value by the predetermined value K3 or greater). If the deviationD is less than or equal to the predetermined value “−K3”, the processadvances to Step 1108, and a value obtained by adding a predeterminedvalue K4 to the previous learning correction amount (n−1) is updated andstored in a rewritable nonvolatile memory such as backup RAM of ECU 38as a present learning correction amount (n). With this arrangement, thelearning correction amount (n) of the learning region Ti correspondingto the present throttle opening degree θ is updated. In this regard, therelationship between the predetermined values “−K3” and “K4” used inSteps 1107 and 1108, respectively, is set as: |−K3|>K4>0.

When a state where the deviation D is less than or equal to thepredetermined value “−K3” (state where the map value is smaller than theactual value by the predetermined value K3 or greater) continues, thelearning processing in Step 1106 is repeated and the learning correctionamount (n) gradually increases in the positive direction.

In contract, both in Steps 1105 and 1107, when the answers are No,namely, when it is determined that K1>deviation D>−K3, the processadvances to Step 1109 and the previous learning correction amount (n−1)is updated and stored as it is in the rewritable nonvolatile memory suchas backup RAM of ECU 38 as a present learning correction amount (n).

Further, the learning method of the learning correction amount (n) maybe modified as required, such as setting the learning correction amount(n) by using a map etc. according to the deviation D.

During the engine operating state, ECU 38 searches the map of thethrottle flow rate parameter μ·A stored in the ROM (storage means),reads the map value of the throttle flow rate parameter μ·Acorresponding to the present throttle opening degree θ, and corrects themap value by using the learning correction amount. Then, by using themap value after correction, ECU 38 calculates a throttled air quantityGin to calculate a cylinder charged air quantity Gcf.

According to the present embodiment described above, when apredetermined learning execution condition is fulfilled, by using theequation derived from the equation for calculating the throttled airquantity of the intake model, the actual value of the throttled flowrate parameter μ·A corresponding to the present throttle opening degreeθ is calculated. Based on the deviation D between the actual value andthe map value (adaptation value), a learning correction amountcorresponding to the map value is learned. Then, during the engineoperating state, the map value of the throttle flow rate parameter μ·Acorresponding to the present throttle opening degree θ is corrected byusing the previous learning correction amount. After that, by using thecorrected map value, the cylinder charged air quantity is calculated.Therefore, even when a difference is caused between the map value(adaptation value) of the throttle flow rate parameter μ·A and theactual value of the throttle flow rate parameter μ·A in an actualvehicle due to manufacture dispersion or aging of parts of the intakesystem and the throttle opening sensor 15, the map value of the throttleflow rate parameter μ·A can properly be corrected by using the learningcorrection amount learned based on the deviation D between the actualvalue and the map value. As a result, accuracy of the throttle flow rateparameter μ·A can be improved by simple processing. Further, whilemeeting the demand for load reduction in calculation by ECU 38,calculation accuracy of the cylinder charged air quantity can beimproved, and dispersion of drivability of vehicles and dispersion ofemission can be reduced.

The present invention can be applied to the engine with a superchargerhaving a throttle upstream pressure sensor. In a system having thethrottle upstream pressure sensor, a throttle upstream pressure Pthrupcan be detected by the throttle upstream pressure sensor. Therefore,even in an operation range where a charged pressure by the supercharger25 occurs, the learning correction amount can be learned.

Further, the present invention can be applied to a naturally aspiratedengine without a supercharger. When the present invention is applied tothe naturally aspirated engine, a steady operation state where a changein the intake air quantity is small may be defined as the learningexecution condition. During the steady operation state, a state wherethe relationship between the throttle opening degree and the throttleflow rate parameter μ·A can be regarded as substantially constantcontinues. Therefore, by using an equation derived from the equation forcalculating a throttled air quantity of the intake system model, theactual value of the throttle flow rate parameter μ·A can be calculatedaccurately.

Also, in a system having throttle upstream pressure estimatorcalculating the throttled air quantity of the intake system model, themap value of the throttle flow rate parameter μ·A may be correctedduring the engine operating state by using the learning correctionamount, and the corrected map value may be substituted for the equationderived from the intake system model to calculate the throttle upstreampressure Pthrup.

FIG. 15 is a time chart showing a difference between a value of thethrottle upstream pressure Pthrup estimated by using the intake systemmodel and an actual value (simulation value) and a learning correctioneffect. It is conceivable that the difference is caused by a differencetaking place between the map value (adaptation value) of the throttleflow rate parameter μ·A and the actual value of the throttle flow rateparameter μ·A in an actual vehicle due to manufacture dispersion oraging of parts of the intake system, the throttle opening sensor 15, andthe like.

In such a case, if the map value of the throttle flow rate parameter μ·Ais corrected by using the learning correction amount and a throttleupstream pressure Pthrup is estimated by using the corrected map value,as shown in FIG. 15, it becomes possible to allow the estimated value ofthe throttle upstream pressure Pthrup to substantially match the actualvalue (simulation value), improving the calculation accuracy of thethrottle upstream pressure Pthrup.

Further, the present invention can be applied not only to an engine witha supercharger but also to a naturally aspirated engine which is notequipped with a supercharger.

1. A cylinder charged air quantity calculating apparatus for an internalcombustion engine which calculates a cylinder charged air quantity byusing an equation of an intake system model including a throttle flowrate parameter which represents a flow rate parameter depending on athrottle opening degree, the cylinder charged air quantity calculatingapparatus comprising: storage means for staring a map defining arelationship between a throttle opening degree and a throttle flow rateparameter; learning means for determining whether a predeterminedlearning execution condition is fulfilled and for learning, when thepredetermined learning execution condition is fulfilled, a learningcorrection amount with respect to a map value based on a deviationbetween an actual value of the throttle flow rate parameter calculatedaccording to a present throttle opening degree by using the equation ofthe intake system model and the map value of the throttle flow rateparameter read from the storage means; correcting means for correctingthe map value of the throttle flow rate parameter corresponding to apresent throttle opening degree read from the storage means during anoperating state of the internal combustion engine by using the learningcorrection amount; and cylinder charged air quantity calculating meansfor calculating a cylinder charged air quantity by using the map valueof the throttle flow rate parameter corrected by the correcting meansduring an operation of the internal combustion engine, wherein theinternal combustion engine is provided with a supercharger; and thepredetermined learning execution condition is at least: (1) the engineis in a steady operation state in which a change in an intake airquantity is small; (2) the engine is in a low air quantity region inwhich the intake air quantity is less than or equal to a predeterminedvalue; and (3) a pressure ratio Pm/Pthrup of the throttle downstreampressure Pm to the throttle valve upstream pressure Pthrup is less thanor equal to a predetermined value.
 2. A cylinder charged air quantitycalculating apparatus for an internal combustion engine according toclaim 1, further comprising: throttle upstream pressure estimating meansfor estimating throttle upstream pressure by using the equation of theintake system model during an operation of the internal combustionengine; wherein the throttle upstream pressure estimating meansestimates a throttle upstream pressure by substituting the map value ofthe throttle flow rate parameter corrected by the correcting means intothe equation of the intake system model.